1. Field of the Invention
This invention relates to a process for drying semiconductor wafers or similar substrates and in particular relates to a process which maintains the substrates or wafers in a motionless or static situation during the drying procedure. This invention also relates to an apparatus for drying wafers or substrates, which maintains the wafers or substrates in a motionless or static situation during the drying process. Maintaining the wafers or substrates in a static situation during the drying procedure avoids the undesirable generation of particulate which is deleterious to the wafers or substrates.
2. Description of the Prior Art
At present, the majority of the processes available for wafer and substrate drying are based on a spin drying technique. The equipment used is commonly referred to as a spin rinser dryer (SRD). In SRD equipment, the wafers are contained in a carrier which is positioned either at the center or at the periphery of a basket, and the basket is rotated or spun about its axis at high speed. The centrifugal forces generated by high speed rotation strips the droplets of water from the surface of the wafer. During the high speed spin operation, nitrogen or other inert gas may be introduced to generate turbulence in the basket holding chamber assisting the complete removal of droplets from the wafer surface. Heating of the chamber and its contents above ambient temperatures may be used to enhance the drying operation. For example, heat may be introduced in the form of a flow of heated nitrogen or other suitable inert gas or the chamber itself may be equipped with heating elements.
In the SRD process, the high speed spinning of the basket has been found to be a source of generation of particulate which can deposit on and contaminate the wafers or substrates. Generally, the basket and the speed of rotation are designed to minimize relative movement of the wafers in relation to their position within the basket, but some movement of the wafer within the carrier is always possible. Any movement of the wafer substrate with respect to its position within the carrier is likely to generate deleterious particulate. In addition, the turbulence engendered by the introduction of inert gas into the system is further likely to be a source of particulate.
Another type of equipment used for drying of wafers and substrates, referred to as an IPA dryer, involves immersing the wafers in a liquid/gaseous bath of IPA (isopropyl alcohol). The IPA dryer is based on the principle that, since water is miscible with alcohol, the alcohol will mix with and carry away the water present on the surface of the wafer, eventually leaving only a film of alcohol on the wafer. Since the alcohol has a high vapor pressure, it quickly evaporates leaving the surface of the wafer dry. A negative aspect of the IPA drying process is that the alcohol may leave organic residue remaining on the surface of the wafer as it evaporates. Considering the high level of cleanliness required for the surface of the wafers, this is an unacceptable drawback to the IPA drying technique.
In co-pending commonly assigned U.S. patent application No. 06/832,506, filed Feb. 21, 1986, now U.S. Pat. No. 4,736,760, patented Apr. 12, 1988, there is disclosed a method and apparatus for cleaning substrates with megasonic energy and then for separately rinsing and drying the substrates. The rinsing and drying procedure involves immersing the substrates in a rinse solution at ambient or elevated temperature, and then lifting the substrates from the solution at a slow controlled rate of removal. Although this procedure has certain advantageous features over the SRD and IPA processes, there is still need for improvement in providing both equipment and method for rinsing and drying substrates in a static or motionless process, presenting them clean, dry and free of unwanted particulate.
In U.S. Pat. No. 4,577,650, issued Mar. 25, 1986, there is disclosed an apparatus for treating wafers and substrates which comprises a plurality of vessel segments serially nested together and engaged with a fluid inlet and a fluid outlet connected in a wafer treatment fluid flow line. This process has not so far met with commercial acceptance or success, and there is still need for improvement in the drying of such substrates.